Setback gauge



' May 20, 1952 J. H. sREB SETBACK GAUGE Filed Aug. 2s, 1945 FIG. 2

F I G. 4

FIG. l

NVENTOR JULES H. SREB ATTORNEY Patented May 20, 1952 l T ED STAT-E S 2597.758

srisAoK GAUGE -`Ju1es H. vsieb,silver SprinaMi-l assignoriofthe United States of America, as represented by the S ecretary of' theNavy Vzip'piiea'non Augnst'zs, 19215, sefial'No. 613,164

claims. (01173-167) The present Vinvention relates to an improved setback gage for use in vprojectiles to measure maximum-forceproducing acceleration, or the accorn'panying setback reaction, developed by the propelling charge in a-gunbarrel as avprojectile is'discharged from the gun. y n n The `gage is of the type designed to be mounted within the interior of a projectile with its axis lor direction `of operation 'disposed coincidently with the longitudinal axis of the projection `or parallel to it. K

It is 'an object of the invention tovprovide an improved gage, simple and economical and reliable'in operation.

In the 'preferred practice a gun is pointed upwardly, 'a Yretrievable vprojectile equipped with a gage assembly in accordance with the invention is discharged from the gun, and the gage furnishes the desired data upon recovery of the projectile.

1n the accompanying drawings: Y

Fig. 1 is an elevation of a projectile, partly broken away and Vin axial section, showing a setback gage in accordance with the invention installed therein; Y, d

Fig. 2r is an axial sectional View of the -gageLon a `much larger scale, showing it set for operation, with its 'bob member in detailed section to disclose its interior arrangement;

Fig. 3 is a corresponding Vfragmentary sectional view of the gage barrel member and the retrieved gage in registering conditions for indicating the desired measurement; and

Fig. 4 is a perspective view of the bob member, partly broken away, and detached from the gage.

Fig. 1 illustrates the relation o f fthe lgage gen- ""erally'shownat-H toa projectile I2. In the particular "embodiment illustrated in Fig. 1 the in'- str-u'ment is encased within 'a barrel or tubular holder I3,.`preferably of molded plastic material, with 'afcentral longitudinal open well I4, terminating-at itsforward end in an enlarged recess ISF-itreaend 'the weil pn's into a similar but preferably deeper recess I6 designed vto be closed bythe base I1 of the projectile, to form a chamber for the reception and retention of a bob I8. The bob is a mass of metal of predetermined size, shape and weight.

screw25. This arrangement-permits adjustment of the position ofthe rod. The Vfree end of the rodis r`fashioned with a reducedY integral axial extension V26 rforming an abutment orshoulder 21.

The principal component jof the indicating 4means consists of a coil of relatively soft inelastic but ductile wire wound inthe form ofV atight helix, asshownjat 28 in Fig. 2 mounted in the well and supported bythe screw plug parallel with and 'adjacent rod 2t. vindicating element -28 'is essentially a tension springbut is formed of material which is "capable of plasticv deformation, or Lof 'taking'a permanent set `under theforces and at the temperature present during setback. The degree of such deformation is a'measure of the maximum'setback'force. y t l One Vend of the Wire indicator is xed, asv by Welding or soldering 4in agsocket of the Ascrew plug, and 'the free end terminates in a hook 29. The intermediate 4portion ofthe wire, altho shown in the form of a helix, might of course be of other deviouscharacter. Inits initial condition shown in Fig. 1 the indicator coil is located parallel with and adjacent the stem 24; and its hooked end projects rearwardly beyond shoul-derZ'l. VThe indicator wire is `sufficiently stii to be self -sustaining and toresist distortion under the lesser forces to which it may be subjected 'prior to ring. The bob is Aautomatically detached from the wire upon riri'gyaswill presently be indicated in detail, and the wire-is alsor stiff enough to resist further distortiondue to Ytheimpact or landing of the projectile with the'bob detached. Y

The indicator is held in its initial position by the attachment of the bob to the stem 26, and strained zin operation by the setback force acting on lthe bob. 4

Rod 24 and bob I8 are of'such dimensions that when the gage is initially set for operation, the indicator is under 'a slight but predetermined tension within its elastic limit, sufficient to provide a parameter for subsequent computations.

Bob vI'8 is 'formed as a cylinder having a longitudinally extending socket 3|! designed slidably 'to receive extension 26. This socket opens intoan interior transverse channel 3I which extends through the bob at 32 and communicates with a longitudinal channel 33. Channel 33 is designed to receive the hooked end 29 of the coil.

The bob is mounted on extension 26 and abuts shoulder 21. The bob is detachably secured to the hook 29 by a spring wire U-shaped latch 35, one end of which is firmly anchored at the rear end of the bob, and the other end of which ter-` minates in a latch hook 36.

In setting the gage the latch hook 36 is rst pressed through socket 30, and through the transverse channel 3l into channel 33 of the bob, and then the bob is slipped onto extension 26 and up against shoulder 21.

As the bob is slipped on extension 26 the engagement of the extension with the latch forces the latch hook 36 across channel 33 into aperture 32 and by frictional engagement of the bob, the extension and the latch, the bob is retained on the extension.

The hook 29 of the indicator is now inserted in channel 33 and manipulated into engagement with the latch hook 36. The retracted indicator is thus set and held taut for thergaging operation.

The guide pin 26 acts as a keeper or detent for the latch 35, which cooperates with hook 29 to connect the bob, through the coil, to the stationary screw plug as a support.

Under force of setback the bob is pulled rearwardly, thus stretching the coil indicator.V Under continued pull of setback on the bob latch 35 is withdrawn from engagement with extension 26 thus releasing the latch from lateral pressure, but hook 3G still remains latched to hook 29 of the indicator. This frictional engagement of the hook is maintained, and the elongation of the spring continues, until the force of setback reaches its pea-k. The bob continues to hang on the hook until the setback force subsides to a low Value. When a low predetermined value of force or acceleration is reached, spring 35 is enabled to overcome the frictional force between the hooks 36 and 29, so that the latch becomes disengaged and the bob is freed from the extended indicator and deposited in the pocket Hi, as indicated by dotted lines in Fig. 2.

As a result of the setback force the indicator is strained from the condition shown in Fig. 2 to that illustrated in Fig. 3, and the drawn out condition is maintained, even under striking impact of the projectile.

The maximum force due to acceleration of the projectile or setback of the bob developed within the gun barrel is indicated by the increase in length of the indicator caused by movement of the bob. Since strain is a function of stress this elongation may be translated into force units.

-Before loading the gage into a projectile, a measurement of distance is made between any xed stationary reference point as for instance arpoint on rod Zit and the hook 29. The wire is elongated during setback of the projectile. After ring and recovery of the projectile the distance between the previously measured points is again measured. The diierence between the two measurements gives the elongation of the coil. From a calibration curve of elongation or strain Verus force or stress is determined the force that must have acted on the coil during setback of the projectile. The ratio of the peak acceleration of the projectile, to the acceleration of gravity, is obtained by dividing the value of force ccrresponding to the measured elongation, by the Weight of the bob. This factor is commonly designated as the number of g acting on the projectile.

While there has been shown and described what is at present considered to be the preferred embodiment of the invention it will be obvious to those skilled in the art that various changes and modications may be made therein without departing from the true spirit of the invention, and therefore the scope of the invention is defined solely in and by the following claims.

I claim:

1. In a setback gage for use in a missile, the combination of a support member, a deformable indicating member secured at one end to said support member, said indicating member being Iii) made of material that has a small elastic limit, an inertia member releasably held by said support member and transferrable to the remaining end of said indicating member, when setback occurs, whereupon said inertia member imposes upon said deformable indicating member stresses very greatly exceeding its elastic limit, thereby permanently deforming said indicating member, releasable means retaining the inertia member resiliently in engagement with the deformable member before and during the setback period, and means coacting with the support member and the inertia member for initially preventing the release of said releasable means.

2. The combination deiined in claim l, wherein the deformable indicating member is initially a closely-wound helix made of metal wire.

3. The combination defined in claim l, wherein additionally guide means are provided on the support member, for guiding the inertia member while under the inuence of the setback force.

4. The combination dened in claim l, wherein the support member has a portion that constitutes a guide for the inertia member, said inertia member being slidably mounted on said portion.

5. The combination dened in claim l, wherein the deformable indicating member has its unsecured end formed as a hook and wherein the inertia member is provided with a latch that frictionally engages said hook, and means coacting with the support member and the inertia member are provided, for initially retaining the latch in engagement with said hook.

JULES H. SREB.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,370,784 Edwards Mar. 6, 1945 2,377,212 Cottrell May 29, 1945 2,385,116 Trimbach Sept. 18, 1945 FOREIGN PATENTS Number Country Date 292,516 Great Britain Sept. 19, 1929 

